


let me be empty

by overlordy



Category: Undertale (Video Game)
Genre: Angst, Body Horror, Bone Fondling, Dom!Sans, Fluff, M/M, PWP, Plot What Plot/Porn Without Plot, just a little bit, sub!Gaster, um, what is going on in this fic, you'll never guess what song i got the title from
Language: English
Status: Completed
Published: 2015-12-19
Updated: 2015-12-19
Packaged: 2018-05-07 14:27:04
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 1,758
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/5459747
Author URL: https://archiveofourown.org/users/overlordy/pseuds/overlordy
Summary: <blockquote class="userstuff">
              <p>Sans just wants to show Gaster how much he means to him.</p>
            </blockquote>





	let me be empty

**Author's Note:**

> what exactly am i doing? i will never know. never.  
> anyway enjoy this sin i guess woohoo

Slimy appendages trail along Sans’s femur, their movements gentle and teasing. Sans breathes out, his voice catching as another slick tendril wraps around his ribcage. He keens as pleasure seeps into his bones. It feels odd. Temporary.

Something’s off.

“stop.”

Gaster withdraws his tentacles immediately, letting Sans sink to the ground.  ** “What… What is the matter, Sans?”  ** he asks. His eye sockets furrow in concern.  ** “Did I… Do something wrong?” **

Sans sighs and crosses his arms over his exposed chest. Gaster sits back and waits patiently as Sans collects his thoughts. The smaller skeleton feels a coldness creeping into his bones.

“how long?”

_ “ _ ** I… Beg your pardon?” **

“how long’s this gonna to last? how long is it gonna be until i can see you again?” Sans grips his arms tightly to hide his shaking hands and plasters a smile on his face, like he wasn't tired of it all. “i mean, don’t get me wrong. i love being able to see you at all, but… sometimes i miss you too much, yknow?”

He pauses. Gaster remains silent. If Sans didn't know better, he would assume his old partner had up and left him. He wouldn't, he would never. Not again.

“let me… let me show you. let me show you how much you mean to me.”

The silence persists, heavy and oppressive and Sans wonders if he made a mistake. Sweating, his resolve stumbles. “i-i mean, you don't have to, just me bein’ a bonehead, i guess, heh-”

** “Sans…” **

“uh, yeah buddy?”

** “If you wish, then you may… Show me,”  ** Gaster says, his tremulous voice echoing in Sans’s skull.  ** “I trust you.” **

Sans feels his face flushing into an embarrassing blueberry color. “i, uh, are you sure? i mean…”

** “I am very sure, Sans,”  ** Gaster chuckles, directing a slimy tendril to move upwards and caress Sans’s cheek.  ** “Do… Whatever you like. I look forward to it.” **

Sans exhales and nods, feeling heat returning to his bones as Gaster settles back and beckons the smaller skeleton to climb on top of him. Sans stares down at the former scientist, filled with an unforeseen amount of nervousness. He doesn't know where to start.

He straddles Gaster's waist, the sensation isn't far from sitting on a particularly warm waterbed, and considers as Gaster watches him with a saintly amount of patience. His body is relatively shapeless; a swirling and shifting pile of dark that hurts to look at for too long, but Sans loves it. He loves every inch of Gaster, from his brilliant mind to his dorky laugh to the cracks on his skull he's always so self-conscious of. Sans decides to begin there, bending down and first pressing his teeth against the upper crack. Sans feels Gaster jolt in surprise and he pulls back, soon replacing his teeth with his hand. The former scientist hums and closes his eyes as Sans massages his temples and traces his fingers along the length of the fissure.

“you're beautiful, G,” Sans breathes. He watches as Gaster's face turns an attractive shade of muted purple.

** “I wouldn't call these old bones… Beautiful,”  ** Gaster replies, his hands coming up to grip Sans’s hips.

The smaller skeleton chuckles and summons his magic with practiced ease. “well good thing i’m here to do it.” He parts his jaws, his electric blue tongue sliding out of his mouth. His hands frame Gaster’s face as he licks a long stripe along the crack in Gaster's skull.

** “Ah… S-Sans-” ** another thorough stroke of his tongue has the former scientist choking on a withheld moan and trembling against him.

God, he sounds gorgeous. Arousal lingers hot and heavy in Sans’s bones as he moves his hands down to Gaster’s neck, hidden by the collar of a fluffy white turtleneck. He finds it endearing that out of all the things left behind after Gaster fell, it was his soft sweater.

One finger tugs down the turtleneck and exposes the top of a slender spine that fades into nothingness as soon as it reaches where his shoulders should be. His tongue shifts its attention to the second crack running beneath Gaster’s eye socket as his hands start a slow rhythm stroking and teasing Gaster’s spine. His fingers dance along vertebrae and linger around the edge of the impermeable darkness that swallows the former scientist up. Gaster trembles and gasps, wracked with sensation that he more than likely hasn't felt in years. Decades. Centuries?

Sans never could wrap his mind over Gaster’s scrambled timeline, and he won't try to now.

** “S-aaans,”  ** Gaster moans, his grip tight around his former protégé’s hips. Sans moves back from Gaster’s skull and devours the sight of his flushed face and open mouth, panting for breath. He shudders.

“wanna move this along, G?” he asks, sounding rather breathless himself. He chuckles. Gaster can get him riled up without even doing anything.

** “Yes, please,”  ** Gaster hisses, and  _ wow _ Sans should get him to say please more often. Gaster shudders violently beneath him and begins to  _ bubble _ and Sans decides to file that thought away for a later date as his voidal boyfriend decides it would be a great idea to imitate a glass of soda.

“uh- what-” he stutters as Gaster shifts underneath him. Disembodied hands become arms, a formless torso elongates until Sans is sitting atop a nearly exact, if a little monochrome, copy of Gaster's old body.

Gaster smiles up at him, calm and collected as ever.  ** “I thought this might make it easier. For both of us.” **

He might cry. He gazes at Gaster, eyes raking in his pitch black rib cage, the delicate curve of his clavicle, all connected to a long and slender spine and he can feel memories flooding back by the bucket load. It's almost too much.

“h-how long have you been able to do this, huh?”

** “Oh, I did not know I could until now.” **

“and it doesn't take too much energy?”

** “Not too much. I can likely maintain this shape for a few hours, but it is not permanent.” **

“that's good enough for me, G,” Sans laughs. “and you can still feel everything?”

** “Well, yes, it is still my matter, just arranged differently.” **

“so, you can feel this?” Sans trails the tip of his finger down a black sternum and Gaster moans, quiet and deep.

** “I-it appears so. Forgive me, it has been a long time since I have felt… this. I am, er, quite sensitive.” **

“would you say you’re…  _ sans _ itive?”

Gaster chuckles but the sound tapers off into a strangled groan as Sans grips his ribs with both hands. He shivers and gasps and pants, breaths hot and heady, as Sans twists his fingers through delicate and sensitive bones, stroking around the edges and pressing hard. Gaster whines, his spine arching off the ground. Sans watches, enchanted, and can almost count each individual vertebrae before Gaster squirms underneath him and he realizes he was so distracted he stopped.

“getting impatient?” Sans teases, freeing one hand from Gaster’s rib cage and reaching up to caress his flushed cheek. With his other hand he grips the base of Gaster’s spine, just above his pelvis, and strokes long and slow all the way back up to his ribs. Gaster throws his head back and cries out, his arms wrapping around Sans’s shoulders and his fingers digging hard into his scapula. The sensation tingles just slightly and Sans represses a noise, focusing all of his energy into making Gaster come apart under his fingers. Judging by the way the former scientist is gasping and shuddering with every languid stroke of his spine, Sans is really doing a bang-up job.

Heh, bang. Good one.

“that feel good, G?” Sans asks, voice low and quiet. Gaster whimpers. “guess so, judging by the sounds you’re making.”

** “S-Sans…”  ** Gaster breathes, so wanton and full of longing that it shoots a thrill along Sans’s spine.

“heh, i know, big guy. i got you.” Gaster smiles fondly and Sans wastes no more time. He’s teased Gaster for long enough. He fits his pelvis snugly against Gaster’s and glances up. The former scientist nods his head, and Sans rolls his hips. Heat blossoms at the base of his spine as sensitive bones rub together, a little dry but still perfect. Sweats beads along Sans’s forehead as he sets a steady pace.

Gaster tosses his head side to side, his hand gripping Sans’s shoulders like a lifeline as he loses himself to pleasure. Tiny, choked moans fall from his mouth, his voice trembles and cracks and  _ god _ , he missed this. Sans’s hands find Gaster’s ribs again and stroke and caress with unhurried movements as the pace of his hips quicken. Gaster’s cries increase in volume with each subtle movement, it almost sounds like he’s in pain.

“G?” Sans asks, his breaths coming quick and heavy.

** “A-ahh… Sans! Don’t- don’t stop, please!” **

If Gaster started using contractions then he must be doing a good job. Sans chuckles and mutters “of course” as he parts his jaws and dips his head to run his tongue along Gaster’s sternum. It’s too much for the scientist, who arches up against Sans’s tongue and shudders.

** “Ohh,  _ ah _ , I’m- I’m g-going to-”  ** His voice dies away as his orgasm hits him hard, his entire body trembling under Sans’s touch. The smaller skeleton continues moving his hips, watching as Gaster rides wave after wave of pleasure, his mouth open in a silent cry.

The waves die down and Gaster slumps, boneless- heh- against the ground. Sans stills above him, still panting from exertion. Boy, he really is out of shape. They sit there, tired breaths mingling in the still air. Gaster’s eyes are closed.

“you okay, G?” he asks after the second minute of silence passes. “...did you fall asleep?”

** “N-no, I just needed some time to… gather myself,” ** Gaster sighs, his eyes opening. He stares lovingly up at Sans and reaches up and cups his cheek.  ** “That was incredible. Thank you.” **

“heh, no need to thank me.”

** “Er- do you still need to…?” **

Sans shakes his head and waves the notion off with a flick of his wrist. “nah, i’m good. don’t worry about little ol’ me.”

Sans watches as Gaster’s form begins to crumble away.  ** “Alright… Sans?” **

He tries not to feel hopeless. “yeah G?”

** “I love you.” **

He tries. “me too, you big dork. see you later?”

But, Gaster is already gone, leaving Sans feeling empty in his wake.

“heh… just hit it and quit it like always, huh?”

He tried.

He really did.


End file.
